Disposable paper products have been used as a substitute for conventional cloth wipers and towels. In order for these paper products to gain consumer acceptance, they must closely simulate cloth in both perception and performance. In this regard, consumers should be able to feel that the paper products are at least as soft, strong, stretchable, absorbent, and bulky as the cloth products. Softness is highly desirable for any wipers and towels because the consumers find soft paper products more pleasant. Softness also allows the paper product to more readily conform to a surface of an object to be wiped or cleaned. Another related property for gaining consumer acceptance is bulkiness of the paper products. However, strength for utility is also required in the paper products. Among other things, strength may be measured by stretchability of the paper products. Lastly, for certain jobs, absorbency of the paper products is also important. As prior art shows, some of the above-listed properties of the paper products are somewhat mutually exclusive. In other words, for example, if softness of the paper products is increased, as a trade-off, its strength is usually decreased. This is because conventional paper products were strengthened by increasing interfiber bonds formed by the hydrogen bonding and the increased interfiber bonds are associated with stiffness of the paper products. Another example of the trade-off is that an increased density for strengthening the conventional paper products also generally decreases the capacity to hold liquid due to decreased interstitial space in the fibrous web.
To control the above trade-offs, some attempts had been made in the past. One of the prior art attempts to increase softness in the paper products without sacrificing strength is creping the paper from a drying surface with a doctor blade. Creping disrupts and breaks the above-discussed interfiber bonds as the paper web is fluffed up. As a result of some broken interfiber bonds, the creped paper web is generally softened. Other prior art attempts at reducing stiffness in the paper products include chemical treatments. Instead of the above-discussed reduction of the existing interfiber bonds, a chemical treatment prevents the formation of the interfiber bonds. For example, some chemical agent is used to prevent the bond formation. In the alternative, synthetic fibers are used to reduce affinity for bond formation. Unfortunately, all of these past attempts failed to substantially improve the trade-offs and resulted in the accompanying loss of strength in the web.
Further attempts were made to reinforce the weakened paper structure that had lost strength after the above-discussed treatments. The web structure can be strengthened by applying bonding materials to the web surface. However, since the bonding material generally reduces the interstitial space, the bonding application also reduces absorbency in the web structure. In order to maintain the absorbency characteristic, as disclosed in U.S. Pat. Nos. 4,158,594 and 3,879,257 (hereinafter the '257 patent), the bonding material may be advantageously applied in a spaced-apart pattern, and the applied area is followed by fine creping for promoting softness. Although these improvements are useful for light paper products such as tissue and towel, it is less suitable for heavier paper products which require higher abrasion resistance and strength.
One of the commonly used techniques to solve the above problem is to laminate two or more conventional webs with adhesive as disclosed in U.S. Pat. Nos. 3,414,459 and 3,556,907. Although the laminated multi-ply paper products have the desirable bulk, absorbency and abrasion-resistance for heavy wipe-dry applications, the multi-ply products require complex manufacturing processes.
In the alternative, to increase abrasion resistance and strength without sacrificing other desirable properties and complicating the manufacturing process, the '257 patent discloses the bonding material applied to a web in a spaced-apart pattern. The web structure used in the '257 patent includes only short fibers and a combination of short fibers and long fibers and forms a single laminar-like structure with internal cavities. Some short fibers are randomly oriented in the cavities to bridge outer layers so as to enhance abrasion resistance. At the same time, the remaining space in the cavity provides high absorbence. Although the '257 patent anticipated heavy uses, industrial applications require durable and highly absorbent paper products. The '257 patent used long fibers for enhancing only the strength of the web structure. However, such heavy duty paper products necessitate the web structure with a higher total water absorption ("TWA") and a higher abrasion resistance while retaining bulk and other desirable properties.
The U.S. Government has recently mandated that wipers sold to any U.S. Government Agencies must contain 40% of post consumer fiber (recycled fiber). In addition, the EPA may eventually require 40% or more recycled fiber in all wipers sold. One problem with using high percentages (40% or greater) of recycled fiber is that the strength, softness and bulk may be decreased by 20% through 30%. Even when the web containing the recycled fiber is double recreped, the strength, softness and bulk may be less than adequate. Similar inadequate properties arise when using other non-premium fibers including CTMP (chemi-thermomechanical pulp), and unbleached recycled fiber, which have a lower propensity for accepting chemical debonder.
In summary, as discussed above, there remains a number of problems for towel products. The prior attempts have either trade-offs among the desirable properties or require a complex process. It would accordingly be desirable to have an improved process to increase the strength, bulk and softness of the product and allow the production of a product with high percentages of non-premium fibers, including recycled fibers.